The present invention relates to methods and devices for cycling the temperature of a device-under-test, and more particularly to chuck systems for semiconductor wafers that provide for rapidly obtained set-point temperatures over a wide control range.
Thermal testing systems used in the semiconductor industry have advanced to the point that wide temperature variations for device testing can be induced in semiconductor wafers. For example, Temptronic Corporation (Sharon, Mass.) markets a thermal test system called THERMOCHUCK(copyright). This thermal inducing vacuum platform allows for wafer probing, testing, and failure analysis at precise, controlled temperatures. Wafers as big as 300-mm in diameter can be accommodated and temperature controlled with a range of xe2x88x9265xc2x0 C. to +400xc2x0 C.
A modern wafer probing system is described by Warren Harwood, et al., in U.S. Pat. No. 6,313,649 B2, issued Nov. 6, 2001, and titled WAFER PROBE STATION HAVING ENVIRONMENT CONTROL ENCLOSURE. A positioning mechanism is included to facilitate microscopic probing.
Operating temperatures over +200xc2x0 C. and certainly those as high as +400xc2x0 C. resulted in a prior art requirement to valve cooling air and liquid coolant between high temperature and low temperature evaporators. One such arrangement is described by George Eager, et al., in U.S. Pat. No. 4,784,213, issued Nov. 15, 1988, and titled MIXING VALVE AIR SOURCE.
Typical device-under-test chucks used for probing semiconductor wafers have a flat plate with holes in it so the semiconductor wafer can be drawn tightly down with a vacuum. For example, see U.S. Pat. No. 6,073,681, issued to Paul A. Getchel, et al., on Jun. 13, 2000, for a WORKPIECE CHUCK. The flat plate usually has an electric heater and a chiller heat-exchanger for heating and cooling the device-under-test. A fluorocarbon liquid is pumped from an external chiller through the chiller heat-exchanger to bring the temperature down below xe2x88x9265xc2x0 C. The electric heating elements can raise the device-under-test temperature as high as +400xc2x0 C. Thermocouples are used to measure the chuck temperature and provide feedback to a closed-loop control system with a temperature setpoint manipulated by a user.
William Wheeler describes a hot/cold chuck in U.S. Pat. No. 4,609,037, issued Sep. 2, 1986. An electric heater is used in a top plate and a coolant circulating plate below it is brought in contact during the cooling phase. A power and control system for such a device-under-test chuck is described in U.S. Pat. No. 6,091,060, issued Jul. 18, 2000, to Getchel, et al.
Unfortunately, the fluorocarbon liquid pumped from the external chiller through the chiller heat-exchanger is subject to boiling and evaporation loss when the electric heaters are used. Such fluorocarbon liquids are very expensive, and even a teaspoonful loss every temperature cycle can add up to thousands of dollars of expense over a relatively short time.
It is therefore an object of the present invention to provide a method for rapidly heating and cooling a device-under-test.
It is another object of the present invention to provide a vacuum chuck system that is simple and inexpensive to manufacture and operate.
Briefly, a semiconductor-wafer chuck embodiment of the present invention provides for heating and cooling of a device-under-test. It includes a heat-spreader plate with a clamping surface for a semiconductor wafer. A heater is disposed within the heat-spreader plate and provides for temperature elevations. A chiller heat-exchanger independent of the heat-spreader plate provides for heat removal. A position control system is used to move the chiller heat-exchanger in relation to the heat-spreader plate, and thus provide for an adjustment of the thermal resistance and thermal coupling between the two. The heater typically comprises electric heating elements with a controlled power input including full on and off, and the chiller heat-exchanger is moved sufficiently far enough away to prevent boiling and evaporation of a coolant disposed inside when the heater is switched on. A device-under-test-temperature controller has outputs connected to the heater and the position control system, and an input for sensing the temperature of a device-under-test clamped to the heat-spreader plate. It then can control the device-under-test temperature by controlling the heater power, and/or by moving the chiller heat-exchanger in relation to the heat-spreader plate.
An advantage of the present invention is that a method is provided for rapid heating and cooling of devices-under-test.
Another advantage of the present invention is that a hot/cold vacuum chuck system is provided that does not boil off and evaporate coolant, and therefore is inexpensive to operate.
A further advantage of the present invention is that a hot/cold chuck system is provided that avoids the use of complex valving systems for coolant circulation and control, and therefore is less expensive to manufacture.
Another advantage of the present invention is that a hot/cold chuck system is provided that does not depend on valves to route coolant and cool-down air.
A still further advantage of the present invention is that a hot/cold chuck system is provided that does not need to expel vapor, fumes or gases too hot for plastic pipes and pieces to be used.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various drawing figures.